I dunno. The exact specifics of what one can do seem to vary wildly. I mean, here, it's just coating the Avengers in symbiote-gunk, but we've seen in the case of Venom that a symbiote can really, really pump someone's muscle mass up, even though Brock was already pretty muscular. So it's a bit of a weird one. Perhaps the symbiote needs flesh to adhere to. *shrugs*.